An investigation into how an undercover reporter managed to smuggle knives and razor blades through airport security was under way today.

Airport operator BAA said it launched the probe after a journalist from the Daily Express repeatedly breached security measures at Heathrow to expose what he described as "alarming flaws".

The reporter claims he spent two-and-a-half weeks working at the world's busiest airport as a baggage handler for the Menzies Aviation Group, having answered a job centre advert just weeks earlier.

Security staff, he says, ignored alarms as he strode through metal detectors carrying blades hidden in his boots. Security guards, he added, assumed the alert was triggered by his steel toe-capped boots.

"I hid a four-inch blade in a cardboard coffee cup which I even handed to an unsuspecting security guard to avoid taking it through scanning machines," wrote Dennis Rice.

"I wandered freely around high secure areas of the airport completely unchallenged. Shockingly, the reason I was able to breach Heathrow's security repeatedly in this way was often due to the plain laziness and ineptitude of security staff manning the scanners.

"Most astonishingly of all was how easy it was for me to land this job. Within weeks on answering a job centre advert I began at £6.50 an hour. Each day I passed in and out of security gates which checked me for any concealed weapons or devices.

"Each time the metal detectors did their job and let out a loud beep to alert staff to the knives and blades I had concealed in my work boots. But to my amazement I was only given a routine padding down, then waved on."

BAA said today it had made all the relevant checks when Mr Rice first applied for the position, including a search for any criminal convictions and a follow-up of references and referees.

A spokesman said: "We are urgently investigating the allegations that potential weapons have been smuggled through staff security. On every occasion a member of staff enters airside areas they are subject to the same scrutiny as passengers.

"We believe the employer carried out the appropriate reference and background checks in this case and these were verified by BAA. Written references were provided, covering a five-year period."

As an additional precaution BAA will now carry out an audit of recently employed staff at Heathrow to ensure relevant procedures have been taken.

Mr Rice was given the job after referees from "legitimate companies" lied about his background on his behalf, the spokesman added.

But the reporter claims he could easily have been "an active terrorist" and that his investigation proved how readily accessible luggage was to any would-be bomber as it sits unguarded waiting to be loaded on to aircraft.

He said his training consisted of an afternoon tour of the airport by the company's training manager in which he was shown how to cross the runway in order to reach the refuelling depot near the new Terminal Five.